Advances in medical technology and diagnostic techniques have led to improved healthcare. Faster diagnosis leads to better treatment regimes and shorter hospital-stays. However, with the increasing understanding of microbial pathogenesis in humans, particularly the role biofilms play in microbial infections, a closer look must be taken into the efficiency of current diagnostic methods for detecting a biofilm and to determine novel diagnostic techniques that specifically target biofilm infections.
In recent years there has been heightened interest in how microbes form biofilms and in their relevance in a clinical setting. Biofilm infections are problematic in hospitals and contribute to the morbidity and mortality of immunocompromised patients. These infections can range from minor conditions such as boils, kidney stones, and gingivitis to more life-threatening illnesses such as osteomyelitis, endocarditis, pneumonia, medical device failure, and cystic fibrosis infections (Shirtliff et al., 2002; Parsek and Singh, 2003; Mack et al., 2006; Sanderson et al., 2006).
During the formation of a biofilm, planktonic bacteria, which are bacterial cells that are free to move passively or actively through bodily fluids, first attach to a surface (which can be damaged tissue or implanted medical devices), secrete a matrix of exopolymeric substance (EPS) that encase the bacteria, and mature to form heterogeneous communities of microorganisms that are resistant to antibiotics and host defenses. The biofilm community is dynamic and after maturation, clusters or individual cells detach and spread throughout the body (O'Toole et al., 2000). A biofilm can be mono- or polymicrobial and once maturity is reached, resolution is only successful upon debridement of the infected tissue or device. The matrix that surrounds the bacteria plays an important role in its virulence. For example, methicillin-resistant Staphylococcus aureus biofilms are up to 1,000 times more resistant to vancomycin than when they are grown in a planktonic suspension (Jefferson et al., 2005). Also, host immunity is compromised during biofilm infections as white blood cells are capable of penetrating and creating antibodies against a biofilm but the immune system is incapable of resolving the infection (Leid et al., 2002b; Jesaitis et al., 2003; Leid et al., 2005; Brady et al., 2006).
Diagnosis of biofilm infections is currently accomplished though a variety of testing methods. Elevated white blood cell counts and C-reactive protein levels are good indicators of inflammation but these tests are not specific for the presence of biofilm (Trampuz and Zimmerli, 2006). Culturing is one of the most routine methods used in identifying microorganisms causing disease but contamination and long processing times are common problems. The inefficiency of traditional culturing methods to correctly identify microbes is exacerbated with biofilms. For example, biofilm microorganisms are difficult or impossible to culture on standard agar plates (Veeh et al., 2003). Nonetheless, since biofilm organisms are inherently attached to a surface, they are not readily cultured by standard techniques.
There are several non-culturing methods used to diagnose biofilm infections. These include imaging tests such as X-ray, CT scans or MRI and are advantageous because they identify the location of infection. These procedures are most useful when used secondarily to a diagnostic technique that first confirms the presence of an infection (Trampuz and Zimmerli, 2006). Drawbacks of imaging techniques, however, include their lack of ability to differentiate between infection and inflammation as well as the costly equipment required to perform these tests. Specificity of these tests for a particular pathogen are not yet available. Serology based assays are becoming more fashionable and address the problem of insensitivity with the previous techniques described. These assays function on the principle of antigen/antibody interaction and can diagnose infection by identifying antibodies in sera that are not normally present in healthy hosts. However, since S. aureus is such a ubiquitous pathogen, this approach can lead to reduced sensitivity as most of the population has either been colonized or infected by S. aureus. For these reasons, it is important to develop new, rapid, and inexpensive techniques to diagnose biofilm infections.